Lipid nanotube or nanowire sensor

ABSTRACT

A sensor apparatus comprising a nanotube or nanowire, a lipid bilayer around the nanotube or nanowire, and a sensing element connected to the lipid bilayer. Also a biosensor apparatus comprising a gate electrode; a source electrode; a drain electrode; a nanotube or nanowire operatively connected to the gate electrode, the source electrode, and the drain electrode; a lipid bilayer around the nanotube or nanowire, and a sensing element connected to the lipid bilayer.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/338,512 filed Jan. 23, 2006 now U.S. Pat. No. 7,544,978 which claimsthe benefit of U.S. Provisional Patent Application No. 60/646,905 filedJan. 24, 2005 titled “One-dimensional Lipid Bilayers on Carbon NanotubeTemplates.” U.S. Provisional Patent Application No. 60/646,905 filedJan. 24, 2005 and titled “One-dimensional Lipid Bilayers on CarbonNanotube Templates” is incorporated herein by this reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG-48 between the United States Department ofEnergy and the Lawrence Livermore National Security, LLC for theoperation of Lawrence Livermore National Laboratory.

BACKGROUND

1. Field of Endeavor

The present invention relates to sensors and more particularly to alipid nanotube or nanowire sensor.

2. State of Technology

United States Patent Application No. 2004/0253741 by Alexander Star andGeorge Gruner for analyte detection in liquids with carbon nanotubefield effect transistor devices published Dec. 16, 2004 provides thefollowing state of technology information: “A variety of spectroscopicmethods are currently used to detect analytes and monitor chemicalreactions in a liquid environment. These detection methods, whereelectronic signal generation in response to an analyte is mediated by anoptical step, are sensitive to changes in electronic configurations ofthe atoms and molecules involved in such reactions. Electronic detectiondevices with transistor configurations have also been fabricated andused for direct electronic signal generation in response to an analyte,although such techniques however have not yielded fully satisfactoryalternatives to spectroscopic detection. The recent emergence ofnano-scale devices offers the opportunity to effect extremely sensitiveelectronic detection of analytes by monitoring the electronicperformance of such devices as they are exposed to a test sampleenvironment. Field-effect transistors (FETs) fabricated usingsemiconducting single wall carbon nanotubes (nanotube FETs, NTFETs) andtheir electrical performance characteristics have been studiedextensively. The conductance characteristics of carbon nanotubes havebeen found, for example, to be sensitive to the presence of variousgases, such as oxygen and ammonia, and thus nanotubes included in anelectrical circuit can operate as sensitive chemical sensors. NTFETdevices, as well as nanowire-based devices, are promising candidates forthe electronic detection of biological species. The mechanism of theelectrical responsiveness of these devices to the presence of analytesoccurs through transfer of charge between the analyte and the nanotubeconducting channel, as evidenced by experiments involving electrondonating (NH3) and electron withdrawing (NO2) molecules in gas phase.Such nanotube-based devices have also been configured in such a way thatthe gate electrode is provided by a buffer, in this configuration thesedevices can be used as pH sensors.”

United States Patent Application No. 2005/0051805 by Byong Man Kim, etal for microprocessors with improved power efficiency published Mar. 10,2005 provides the following state of technology information: “Nanotubescomprise nanometer scale tubular structures, typically made from a sheetof carbon atoms known as a graphene. They may be single wall ormulti-wall structures. A single-walled carbon nanotube typicallycomprises an elongated, single hollow tube that is about 1 nm indiameter and few-hundreds-nm to few-hundreds-μm in length. Amulti-walled carbon nanotube consists of a plurality of generallyconcentric, hollow tubes of different diameters that can range up to afew hundreds of nanometers. One popular method of synthesizing highquality carbon-nanotube structures uses a chemical vapour depositiontechnique based on a vapour-solid interaction of methane and hydrogenwith a catalyst in a heated environment, as described by J. Kong, H. T.Soh, A. Cassell, C. F. Quate, H. Dai, Nature, 395, 878 (1998). Acarbon-nanotube structure can act as a semiconductor or a metal,depending on its diameter and how it is rolled up from a sheet ofgraphene, and has been demonstrated to be harder than the steel and abetter conductor than copper. Reference is directed to P. McEuen, M.Fuhrer, H. Park, IEEE Transactions on Nanotechnology, 1, 78 (2002).Various devices have been formed from carbon-nanotube structures.Ballistic conduction in nanotube structures has been reported wherenanotubes placed between ferromagnetic contacts were used to demonstratecoherent transport of electron spin, as described by K. Tsukagoshi, B.Alphenaar and H. Ago, Nature, 401, 572 (1999). There have been a numberof reports on the use of nanotube structures as the channel material oftransistors which performed better than state of the art CMOS or SOIprototypes and reference is directed to S. Tans, A. Verschueren, and C.Dekker, Nature, 393, 49 (1998); R. Martel et al., Appl. Phys. Lett., 73,2447 (1998); and A. Javey et al., Nature Materials, published online: 17Nov. 2002; doi:10. 1038/nmat769. Logic functions have also beendemonstrated from assembly of nanotube transistors, as described in V.Derycke, Nano Letters, 1, 453 (2001) and A. Bachtold et al., Science,294, 1317 (2001). A single electron memory was demonstrated in which ananotube channel of a transistor was used as a single electron sensorand manipulator—see M. Fuhrer et al., Nano Letters, 2, 755 (2002). Also,a nanotube channel of a transistor has been used as an IR source, inwhich the IR emission was achieved by recombining electrons and holes inthe nanotube channel, injected from the source and drain of thetransistor, as reported by J. A. Misewich et al., Science 300, 783(2003). The structures described so far are demonstration devices andnot apt to yield consistent device characteristics. Various methods offorming heterojunctions in carbon-nanotube structures have been proposedin an attempt to produce more reliable devices. Heterojunctions formedby adjoining carbon-nanotubes of differently rolled-up layers of closelypacked carbon atoms of different diameters have been proposed in U.S.Pat. No. 6,538,262 to V. Crespi et al. Structures utilizing mechanicaldeformation i.e., by straining or bending are described in U.S. patentapplication Ser. No. 20020027312 A1, Mar. 7, 2002. Chemical doping ofcarbon-nanotube structures has been proposed by C. Zhou, Science, 290,1552 (2000) to B. Yakobson. Also, a method of forming a heterojunctionin a nanotube structure by means of a heat induced solid-solid diffusionand chemical reaction is described in U.S. Pat. No. 6,203,864 to Y.Zhang and S. Iijima. However, these junction forming techniques are notparticularly suited to forming transistor structures. U.S. patentapplication Ser. No. 20030044608 A1 by H. Yoshizawa discloses a numberof nanotube structures in which an outer graphene sheet is chemicallymodified to change its conductive characteristics, but the resultingstructure does not exhibit a transistor action. It has been proposed touse Y-shaped nanotube structures to form transistors as described inU.S. Pat. No. 6,325,909 to J. Li et al. The transistor action resultsfrom heterojunctions formed by structural defects in the vicinity of theconfluence of the arms of the Y-shaped nanotube and so the device lacksreproducibility. Also, transistors comprising vertically extendingnanotube structures have been proposed in U.S. Pat. No. 6,515,325 to W.Farnworth, and U.S. Pat. No. 6,566,704 to W. Choi et al. However,vertical nanotube structures are known to include a high density ofvarious defects and exhibit poor semiconductor properties, degradingperformance of the transistor.”

SUMMARY

Features and advantages of the present invention will become apparentfrom the following description. Applicants are providing thisdescription, which includes drawings and examples of specificembodiments, to give a broad representation of the invention. Variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art from this descriptionand by practice of the invention. The scope of the invention is notintended to be limited to the particular forms disclosed and theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

Microfluidics is a multidisciplinary field comprising physics,chemistry, engineering, and biotechnology that studies the behavior offluids at the microscale and mesoscale, that is, fluids at volumesthousands of times smaller than a common droplet. It is a new science,having emerged only in the 1990s, so the number of applications for thistechnology is currently small. However, it is potentially significant ina wide range of technologies. Microfluidics is used in the developmentof DNA microarray technology, micro-thermal and micro-propulsiontechnologies, and lab-on-a-chip technology. Microfluidics also concernsthe design of systems in which such small volumes of fluids will beused. The behavior of fluids at the microscale can differ from‘macrofluidic’ behavior in that factors such as surface tension, energydissipation, and electrokinetics start to dominate the system.Microfluidics studies how these behaviors change, and how they can beworked around, or exploited for new uses. A microfluidic device can beidentified by the fact that it has one or more channels with at leastone dimension less than 1 mm.

Nanowires and nanotubes provide a critical enabling technology forchem/bio sensing. Their surface-to-volume ratio is phenomenally high;therefore, surface events such as binding of a protein or an ion cantrigger a significant change in bulk electronic properties and enableelectrical detection of binding events.

The present invention provides a sensor apparatus comprising a nanotubeor nanowire, a lipid bilayer around the nanotube or nanowire, and asensing element connected to the lipid bilayer. The present inventionalso provides a biosensor apparatus comprising a gate electrode; asource electrode; a drain electrode; a nanotube or nanowire operativelyconnected to the gate electrode, the source electrode, and the drainelectrode; a lipid bilayer around the nanotube or nanowire, and asensing element connected to the lipid bilayer.

The lipid bilayer nanotube or nanowire sensor can detect variations inion transport through a protein pore using the lipid bilayer nanotube ornanowire sensor. The lipid bilayer nanotube or nanowire biosensorprovide superior detection efficiency by using signal amplification, andalso permit straightforward integration and multiplexing. The lipidbilayer nanotube or nanowire biosensor also provide a large amount offlexibility allowing seamless integration with different types ofmembrane-based sensing agents. The lipid bilayer nanotube or nanowiresensor and the biosensor device feature high selectivity, low cost andlow power consumption, and can serve as a wearable “bio-smoke alarm.”

The invention is susceptible to modifications and alternative forms.Specific embodiments are shown by way of example. It is to be understoodthat the invention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate specific embodiments of theinvention and, together with the general description of the inventiongiven above, and the detailed description of the specific embodiments,serve to explain the principles of the invention.

FIG. 1 illustrates one embodiment of a microfluidic device constructedin accordance with the present invention.

FIG. 2 shows the lipid bilayer-carbon nanotube transistor in greaterdetail.

FIG. 3 is a section view of the lipid bilayer-carbon nanotubetransistor.

FIG. 4 illustrates the operation principle of the microfluidic device.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, to the following detailed description, and toincorporated materials, detailed information about the invention isprovided including the description of specific embodiments. The detaileddescription serves to explain the principles of the invention. Theinvention is susceptible to modifications and alternative forms. Theinvention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

Referring now to FIG. 1, one embodiment of a microfluidic deviceconstructed in accordance with the present invention is illustrated. Themicrofluidic device system is designated generally by the referencenumeral 100. Microfluidics is a multidisciplinary field comprisingphysics, chemistry, engineering and biotechnology that studies thebehavior of fluids at the microscale and mesoscale; that is, fluids atvolumes thousands of times smaller than a common droplet. It is a newscience, having emerged only in the 1990s, so the number of applicationsfor this technology is currently small. However, it is potentiallysignificant in a wide range of technologies. Microfluidics is used inthe development of DNA microarray technology, micro-thermal andmicro-propulsion technologies, and lab-on-a-chip technology.Microfluidics also concerns the design of systems in which such smallvolumes of fluids will be used. The behavior of fluids at the microscalecan differ from ‘macrofluidic’ behavior in that factors such as surfacetension, energy dissipation, and electrokinetics start to dominate thesystem. Microfluidics studies how these behaviors change, and how theycan be worked around, or exploited for new uses. A microfluidic devicecan be identified by the fact that it has one or more channels with atleast one dimension less than 1 mm.

Nanowires and nanotubes provide a critical enabling technology forchem/bio sensing. Their surface-to-volume ratio is phenomenally high,therefore surface events such as binding of a protein or an ion cantrigger a significant change in bulk electronic properties and enableelectrical detection of binding events.

The microfluidic device 100 includes a PDMS microfluidic channel 101formed in a base 102. An upper section 103 covers the PDMS microfluidicchannel 101. A gate 104, a source 105, and a drain 106 are located inthe PDMS microfluidic channel 101. A lipid bilayer-carbon nanotubetransistor 107 is connected to the gate 104, source 105, and drain 106by connectors 108 and 109.

Additional lipid bilayer-carbon nanotube transistors can be included inthe system 100 to provide an array of nanotube transistors. For example,the system 100 also includes a lipid bilayer-carbon nanotube transistor107′. The lipid bilayer-carbon nanotube transistor 107′ is connected tothe gate 104, a source 105′, and a drain 106′ by connectors 108′ and109′.

Referring now to FIG. 2, the lipid bilayer-carbon nanotube transistor107 is shown in greater detail. The lipid bilayer-carbon nanotubetransistor 107 comprises a nanoelement 110, a hydrophilic cushion 111,and a lipid bilayer 112. The nanoelement is shielded with the lipidbilayer 112. The hydrophilic cushion 111 is located between nanoelementand the lipid bilayer 112. In one embodiment the nanoelement 110 is asingle-wall carbon nanotube 110. In another embodiment the nanoelement110 is a multi-wall nanotube 110. In another embodiment the nanoelement110 is a nanowire 110. In another embodiment the nanoelement 110 is aninorganic nanowire 110.

The lipid bilayer-carbon nanotube transistor 107 includes a sensingelement 113. The sensing element 113 in one embodiment is a sensing ionchannel 113 connected to the lipid bilayer 112. The sensing element 113in another embodiment is a membrane agent. The sensing element 113 inanother embodiment is a natural bilayer pore. The sensing element 113 inanother embodiment is a synthetic bilayer pore. The sensing element 113is connected to the lipid bilayer 112 and the lipid bilayer 112 servesas a matrix for the sensing element 113. The nanotube 110 generates thesensor readout and the lipid bilayer 112 provides the selectivity to theanalyte.

Referring now to FIG. 3, a section view of one embodiment of the lipidbilayer-carbon nanotube transistor 107 is shown. The single-wall carbonnanotube 110 is surrounded by the hydrophilic cushion 111 and the lipidbilayer 112. The sensing element 113 is connected to the lipid bilayer112. The lipid bilayer 112 serves as a matrix for the sensing element113.

The structural details of the microfluidic device 100 constructed inaccordance with the present invention having been described andillustrated in connection with FIGS. 1, 2, and 3, the operation of themicrofluidic device 100 will now be considered. The lipid bilayer-carbonnanotube transistor 107 is suspended between source electrode 105 anddrain electrode 106. The gate electrode 104 is on the bottom of thechannel 101. The whole device 100 is covered with a PDMS mold withmicrofluidic channels.

The lipid bilayer-carbon nanotube transistor 107 provides a nanoscalebiosensor for detection of pore-forming biological toxins. The lipidbilayer-carbon nanotube transistor 107 incorporates the individualcarbon nanotube 110 surrounded by the lipid bilayer 112. The lipidbilayer 112 serves as a highly-selective membrane controlling access tothe nanotube 110 surface. Toxins disrupt the bilayer's 112 shieldingability and changes the nanotube's 110 conductance. The lipid bilayer112 serves as a tunable semi-permeable membrane controlling the accessto the nanotube 110, and the nanotube conductance provides a readoutmechanism.

The main sensing element of the system 100 is the carbon nanotubefield-effect transistor (FET) 107 with a single-wall carbon nanotube 110connecting the source 105 and drain electrodes 106. The carbon nanotube110 is wrapped in a lipid bilayer shell 112 that houses the sensingelement 113 proteins. The bilayer 112 also insulates the nanotube 110surface from the solution providing a barrier to non-specificinteractions. The lipid bilayer 112 does not contact the nanotube 110directly; instead, it rests on a thin permeable polymer cushion 111adsorbed on the nanotube 110.

The microfluidic device 100 will detect the presence of pore-formingbacterial toxins, since many toxins attack cells by incorporating intothe membrane and forming a channel through which the other componentscan either enter the cell or leak out of the cell. When the microfluidicdevice 100 is exposed to a solution of a redox species in the absence ofthe toxin, the lipid bilayer 112 blocks the access to the nanotubes 110.When the toxin incorporates into the bilayer 112 and opens up a pore,the redox species are able to penetrate and bind to the nanotube 110surface, changing the nanotube's 110 conductance and triggering thesensor readout.

The sensing principle exploits the high sensitivity of carbon nanotubetransistors to gating by the external electric fields. Current flowthrough the ion channel 113 in the lipid shell 112 modulates theelectric field in the vicinity of the nanotube 110 and produces a largemodulation of the transistor current. Alterations of the transportthrough the ion channel 113 change transistor 107 current, which isrecorded by an external circuit. The device 100 is also able to detecttransport events through a single channel 101 with a signal/noise ratioof more than 100. This high efficiency is a direct consequence of twothe following two advantages: (a) large gain achieved with thetransistor configuration and (b) direct electrical interfacing ofbiological ion channels to a reporting nanostructure.

The system 100 provides a biosensor that can detect variations in iontransport through a protein pore using the lipid bilayer-carbon nanotubetransistor 107. The system 100 provides superior detection efficiency byusing signal amplification, and also permits straightforward integrationand multiplexing. The system 100 also provides a large amount offlexibility allowing seamless integration with different types ofmembrane-based sensing agents. The microfluidic device 100 features highselectivity, low cost and low power consumption, and can serve as awearable “bio-smoke alarm.”

Referring now to FIG. 4, the operation principle of a microfluidicdevice constructed in accordance with the present invention isillustrated. The microfluidic device is designated generally by thereference numeral 400. The microfluidic device 400 can be brieflydescribed as a carbon nanotube encapsulated by a lipid bilayer restingon a hydrophilic “cushion” layer. The bilayer supports the sensing ionchannels and also acts as an “insulating jacket” to shield the nanotubefrom the solution species. This insulated carbon nanotube “wire” issuspended between microfabricated source and drain metal electrodes,forming a channel region of a field-effect transistor. The nanotube issuspended across a microfluidic channel with the third “gate” electroderunning on the bottom of the channel.

The microfluidic device 400 includes a gate 401, a source 402, and adrain 403 located in a PDMS microfluidic channel 404. A lipidbilayer-carbon nanotube transistor 405 is connected to the gate 401,source 402, and drain 406 by connectors 408 and 409. The microfluidicdevice 400 and the lipid bilayer-carbon nanotube transistor 405 havemany uses. For example, uses of the microfluidic device 400 and thelipid bilayer-carbon nanotube transistor 405 can be the uses of thedevices illustrated in United States Patent Application No. 2004/0253741by Alexander Star and George Gruner for analyte detection in liquidswith carbon nanotube field effect transistor devices published Dec. 16,2004 and United States Patent Application No. 2005/0051805 by Byong ManKim, et al for microprocessors with improved power efficiency publishedMar. 10, 2005. United States Patent Application No. 2004/0253741 byAlexander Star and George Gruner for analyte detection in liquids withcarbon nanotube field effect transistor devices published Dec. 16, 2004and United States Patent Application No. 2005/0051805 by Byong Man Kim,et al for microprocessors with improved power efficiency published Mar.10, 2005 are incorporated herein by reference.

The main sensing element of the microfluidic device 400 is the lipidbilayer-carbon nanotube transistor 405. The lipid bilayer-carbonnanotube transistor 405 comprises a single-wall carbon nanotube 406surrounded by a hydrophilic cushion 407 and the lipid bilayer 408. Onlyone side of the bilayer 408 is shown; in the device the bilayer 408, andthe hydrophilic cushion 407 encircle the nanotube 408. An ion channel409 is connected to the lipid bilayer 408. The lipid bilayer 408 servesas a matrix for the ion channel 409.

A constant small DC bias illustrated by the circuit 410 and the currentmeter 411 is applied between the source 402 and drain 403 electrodes ofthe nanotube field effect transistor 405. A small AC modulation 412 isapplied to the gate electrode 401 located in the solution 413surrounding the lipid-coated carbon nanotube 405 supporting thebiological ion channel 409. Current through the ion channel 409modulates the double layer surrounding the carbon nanotube and gates thenanotube. Changes in the source drain current are recorded by thecurrent meter 411.

The sensing principle exploits the high sensitivity of carbon nanotubetransistors to gating by the external electric fields. Current flowthrough the ion channel 409 in the lipid shell 408 modulates theelectric field in the vicinity of the nanotube 406 and produces a largemodulation of the transistor current. Alterations of the transportthrough the ion channel change transistor current, which is recorded byan external circuit 410. The microfluidic device 400 detects transportevents through a single channel with a signal/noise ratio of more than100. This high efficiency is a direct consequence of two advantages:platforms: (a) large gain achieved with the transistor configuration and(b) direct electrical interfacing of biological ion channels to areporting nanostructure.

The nanotube FET 405 is gated by the electrical double layer 408 formingaround the nanotube 406. The voltage drop across the double layerdetermines the effective gate voltage. For a given gate electrodevoltage, the voltage drop across the double layer is determined by thebalance of the impedances of the different circuit components: if thedouble layer impedance is large compared to the total impedance, most ofthe voltage drop occurs at the double layer. In this situation;application of an AC bias to the gate electrode will cause a largemodulation of the source-drain current of the FET. If the double-layerimpedance is small compared to the total impedance, there will be littleto no modulation of the source-drain current.

Changes in the conductivity of the ion channel will have a large effecton the membrane impedance. When the ion channel is open, the membraneimpedance is small compared to the double layer impedance, resulting ina large source-drain current modulation. When an analyte blocks thechannel, membrane impedance increases and becomes larger than the doublelayer impedance. In this situation the voltage drop in the double layerdiminishes and produces a significantly smaller modulation of transistorcurrent.

The fabrication of functional lipid bilayers on carbon nanotubetemplates will now be described. Single-wall nanotubes are grown on theTEM grids using catalytic CVD synthesis to produce suspended carbonnanotubes suitable for modification process. A polymer coating is formedon these suspended carbon nanotubes by exposing them to the alternatingsolutions of polyanions and polycations.

Formation of a lipid bilayer around a naked carbon nanotube presentschallenges. First, typical diameters of single-wall carbon nanotubesrange from 1-2 nm, which is below a critical curvature of a commonphospholipids bilayer. Second, the hydrophobic nanotube surface promotesthe formation of a monolayer, not the bilayer that is necessary formembrane channel support. To remedy these problems Applicants placed asemi-permeable hydrophilic polymer “cushion” layer between the nanotubeand the bilayer. This layer is important for a number of reasons. First,the polymer provides hydrophilic support surface for the bilayer.Second, the additional polymer layer between the nanotube and thebilayer increases the size of the structure and helps to match the sizeof the support to the critical bilayer curvature. Third, interactions ofthe lipid headgroups with the polymer “cushion” stabilize the bilayerand increase its robustness. Fourth, the polymer “cushion,” whichtypically contains up to 50% water, lifts the membrane from thesubstrate and helps to maintain natural environment for inserted proteinchannels, which may protrude past the bilayer.

The fabrication of functional lipid bilayers on carbon nanotube ornanowire templates is described in co-pending U.S. patent applicationSer. No. 11/338,512 for lipid bilayers on nano-templates filed Jan. 23,2006 by Aleksandr Noy, Alexander B. Artyukhin, Olgica Bakajin, andPieter Stroeve. U.S. patent application Ser. No. 11/338,512 for lipidbilayers on nano-templates filed Jan. 23, 2006 by Aleksandr Noy,Alexander B. Artyukhin, Olgica Bakajin, and Pieter Stroeve isincorporated herein by this reference.

The fabrication of the lipid bilayer on a nano-template will besummarized. The system of fabrication of the lipid bilayer on anano-template includes various forms of nano-templates, lipid bilayers,and polymer cushions. The fabrication will be described with referenceto a nanotube; however, it is to be understood that a nanowire could beused instead of the nanotube.

First, a carbon nanotube is coated with several alternating layers ofoppositely charged polyelectrolytes, followed by the formation of lipidbilayer by vesicle fusion.

Single-wall nanotubes are grown on TEM grids using catalytic CVDsynthesis to produce suspended carbon nanotubes suitable formodification process. A polymer coating is formed on these suspendedcarbon nanotubes by exposing them to the alternating solutions ofpolyanions and polycations.

Formation of a lipid bilayer around a naked carbon nanotube presentschallenges. First, typical diameters of single-wall carbon nanotubesrange from 1-2 nm, which is below a critical curvature of a commonphospholipids bilayer. Second, the hydrophobic nanotube surface promotesthe formation of a monolayer, not the bilayer that is necessary formembrane channel support. To remedy these problems, Applicants placed asemi-permeable hydrophilic polymer “cushion” layer between the nanotubeand the bilayer. This layer is important for a number of reasons. First,the polymer provides hydrophilic support surface for the bilayer.Second, the additional polymer layer between the nanotube and thebilayer increases the size of the structure and helps to match the sizeof the support to the critical bilayer curvature. Third, interactions ofthe lipid headgroups with the polymer “cushion” stabilize the bilayerand increase its robustness. Fourth, the polymer “cushion,” whichtypically contains up to 50% water, lifts the membrane from thesubstrate and helps to maintain natural environment for inserted proteinchannels, which may protrude past the bilayer.

The 1-D Bilayer formation is started by creating supported lipidbilayers on the “cushioned” carbon nanotubes using vesicle fusion. Themultilayer polymer cushion on nanotubes with a cationic layer (PDDA orPAH) to stabilize the bilayer that contains 75% of the anionic lipid(SOPS). To enable visualization of the final structure, the vesiclesincorporated a small fraction of a fluorescent lipid probe (BODIPY-PC).Scanning confocal microscope images of the resulting structures showlinear fluorescent features inside the holes of the TEM grid, whichcorrespond to the lipidcoated carbon nanotubes stretching across thegrid holes. These results indicate that partial strain relief in thedimension of the nanotube axis coupled with the electrostatic attractionof the bilayer to the polymer support is sufficient to stabilize thebilayer in 1-D configuration. Incorporation of charged lipids in themembrane should reject subsequent lipid multilayer formation. Oneimportant feature of a functional lipid bilayer is the ability of thelipid molecules to diffuse along the bilayer plane.

The assembly process is started by modifying pristine suspendedsingle-wall carbon nanotubes with five alternating polymer layerscomposed of strong polyelectrolytes, such aspoly(diallyldimethylammonium chloride) (PDDA), sodiumpoly(styrenesulphonate) (PSS), and poly(allylamine hydrochloride) (PAH.critical (i.e., smallest) inner radius of the lipid bilayer is ca. 5 nm.Polyelectrolytes that form the cushion produce 1 nm thick layers at lowionic strength conditions; therefore, five polymer layers were used tomatch the critical curvature of the bilayer.

TEM images show that five alternating PAH/PSS layers produce smoothcoating on the nanotubes over large distances, with the diameter of thefinal structure of 10-15 nm. Substitution of PAH to PDDA producesrougher coating of 10-30 nm in diameter. Overall, the addition of thepolymer cushion made the size of the nanotubes comparable (and in somecases even larger) to the smallest reported nanoparticles (14 nm) thatcan support lipid bilayers.

Additional exposure to the solution of an agent is used to form theprotein pore. An onomeric bacterial toxin (such as anthrax) results inthe formation of the oligomeric protein pore in the bilayer membrane. Itis to be understood that other agents than the anthrax toxin can beused. The agents can be biowarfare agents or health related agents. Forexample, the agents can include a full spectrum of biowarfare agentsincluding bacteria, viruses and toxins, examples of which includeAnthrax, Smallpox, Plague, Botulism, Tularemia, and Viral hemorrhagicfever. The agents can also include a full spectrum of health relatedagents including bacteria, viruses and toxins, examples of which includeSARS and avian flu. A list of some of the agents is provided in Table 1below.

TABLE 1 List of Agents Abrin Acids (caustics) Adamsite (DM)Americium-241 (AM-241 Ammonia Anthrax (Bacillus anthracis) ArenavirusesArsenic Arsine (SA) Avian flu Bacillus anthracis (anthrax) BariumBenzene Bioterrorism agents Biotoxins Blister agents/vesicants Bloodagens Botulism Brevetoxin Bromine (CA) Bromobezylcyanide (CA) Brucellaspecies (brucellosis) Brucellosis (Brucella species) Burkholderia mallei(glanders) Burkholderia pseudomallei BZ Carbon Monoxide Caustics (acids)Cesium-137 (Cs-137) Chemical agents Chlamydia psittaci (psittacosis)Chlorine (CL) Chloroacetophenone (CN) Chlorobenzylidenemalononitrile(CS) Chloropicrin (PS) Choking/lung/pulmonary agents Cholera (Vibriocholera) Clostridium botulinum toxin Clostridium perfringens Cobalt-60(Co-60) Colchicine New March 15 Coxiella burnetii (Q fever) CyanideCyanogen chloride (CK) Dibenzoxazepine (CR) Digitalis New March 16Diphosgene (DP) Distilled mustard (HD) Ebola virus hemorrhagic fever E.coli 0157:H7 (Escherichia coli) Nipah virus & hautavirus Epsilon toxinof Clostridium perfringens Escherichia coli 0157:H7 (E. coli) Ethyleneglycol Fentanyls & other opioids Francisella tularensis (tularemia)Glanders (Burkholderia mallei) Hydrofluoric acid (hydrogen Fluoride)Hydrogen chloride Hydrogen cyanide (AC) Hydrogen fluoride Incapacitatingagents Iodine-131 (1-131_(—) Lassa fever Lewisite (L, L-2, L-2, L-3)Long-acting anticoagulant Lung/choking/pulmonary agents Marburg virushemorrhagic fever Melioidosis Methyl Bromide Methyl Isocyanate Mudslides& landslides Mustard gas (H) (sulfur mustard) Mustard/lewisite (HL)Mustard/T Nerve agents Nitrogen mustard (HN-1, HN-2 HN-3 Optoids Osmiumtetroxide Paraquat Phosgene (CG) Phostene oxime (CX) PhosphinePhosphorus, elemental, white or yellow Plague (Yersinia pestis)Plutonium-239 (pu-239 Potassium cyanide (KCN) Psittacosis (Chlamydiapsittaci) Pulmonary/choking/lung agents Q fever (Coxiella burnetti)Radioisotopes (radioactive Isotopes) Radioactive isotopes (RadioisotopesRicin toxin from Ricitus communis Rickeittsia prowazekii (typlus Fever)Salmonella species (salmonellosis) Salmonella typhi (typhoid fever)Salmonellosis (Salmonella species) Sarin (GB) SARS Saxitoxin Sesquimustard Shigella (shgellosis) Shigellosis (Shigella) Smallpox (variolamajor) Sodium azide Sodium cyanide (NaCN) Sodium Monofluoroacetate Soman(GD) Staphylococcal enterotoxin B Stibine Stontium-90 (Sr-90) StrychnineSulfuryl Fluoride Sulfur mustard (H) (mustard gas) Super warfarin Tabun(GA) Terodotoxin Thallium Trichothecene New March 17 Tularemia(Francisella tularensis) Typhoid fever (salmonella typhi) Typhus fever(Rickettsia Prowazekii) Uranium-235 (U-235) Uranium-238) U-238 Varioilamajor (smallpox) Vesicants/blister agents Vibrio cholera (cholera) Viralencephalitis Viral hemorrhagic fevers Vomiting agents VX Whitephosphorus Yersinia pestis (Plague)

Single-wall nanotubes are grown on TEM grids using catalytic CVDsynthesis to produce suspended carbon nanotubes suitable formodification process. The polymer coating is formed on these suspendedcarbon nanotubes by exposing them to the alternating solutions ofpolyanions and polycations by layer-by-layer assembly. The lipid bilayeris formed by vesicle fusion. Additional exposure to the solution of anagent results in pore insertion and the formation of the protein pore inthe bilayer membrane.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A nanoscale sensor apparatus for detection of biological toxins,comprising: a base, a microfluidic channel in said base, a gate in saidmicrofluidic channel, a source in said microfluidic channel, a drain insaid microfluidic channel, a lipid bilayer-carbon nanotube or nanowiretransistor in said microfluidic channel, said lipid bilayer-carbonnanotube or nanowire transistor connected to said gate, said source, andsaid drain, said lipid bilayer-carbon nanotube or nanowire transistorincluding a nanotube or nanowire, a lipid bilayer around said nanotubeor nanowire, a hydrophilic cushion between said nanotube or nanowire andsaid lipid bilayer, wherein said hydrophilic cushion is a polymercushion, a sensing element connected to said lipid bilayer, and a covercovering said microfluidic channel.
 2. The sensor apparatus of claim 1wherein said sensing element is a pore.
 3. The sensor apparatus of claim1 wherein said sensing element is a membrane agent.
 4. The sensorapparatus of claim 1 wherein said sensing element is a bilayer pore. 5.The sensor apparatus of claim 1 wherein said sensing element is anatural bilayer pore.
 6. The sensor apparatus of claim 1 wherein saidsensing element is a synthetic bilayer pore.
 7. The sensor apparatus ofclaim 1 wherein said sensing element is a sensing ion channel connectedto said lipid bilayer.
 8. The sensor apparatus of claim 1 wherein saidnanotube or nanowire is a single-wall carbon nanotube.
 9. The sensorapparatus of claim 1 wherein said nanotube or nanowire is a multi-wallcarbon nanotube.
 10. The sensor apparatus of claim 1 wherein saidnanotube or nanowire is a nanowire.
 11. The sensor apparatus of claim 1wherein said nanotube or nanowire is an inorganic nanowire.
 12. Thesensor apparatus of claim 1 wherein said lipid bilayer is a lipidbilayer shell that surrounds said nanotube or nanowire.
 13. The sensorapparatus of claim 1 wherein said sensing element is a protein pore insaid lipid bilayer wherein said protein pore is sensitive to specificagents.
 14. The sensor apparatus of claim 1 wherein said sensing elementis a protein pore in said lipid bilayer wherein said protein pore issensitive to a full spectrum of biowarfare agents including bacteria,viruses and toxins.
 15. The sensor apparatus of claim 1 wherein saidsensing element is a protein pore in said lipid bilayer wherein saidprotein pore is sensitive to a full spectrum of health related agentsincluding bacteria, viruses and toxins.
 16. A nanoscale biosensorapparatus for detection of biological toxins, comprising: a base, amicrofluidic channel in said base, a gate electrode in said microfluidicchannel; a source electrode in said microfluidic channel; a drainelectrode in said microfluidic channel; a lipid bilayer-carbon nanotubeor nanowire transistor in said microfluidic channel, said lipidbilayer-carbon nanotube or nanowire transistor including a nanotube ornanowire operatively connected to said gate electrode, said sourceelectrode, and said drain electrode; a lipid bilayer around saidnanotube or nanowire, a hydrophilic cushion between said nanotube ornanowire and said lipid bilayer, a sensing element connected to saidlipid bilayer, and a cover covering said microfluidic channel.
 17. Thebiosensor apparatus of claim 16 wherein said nanotube or nanowire is asingle-wall carbon nanotube.
 18. The biosensor apparatus of claim 16wherein said lipid bilayer is a lipid bilayer shell that surrounds saidnanotube or nanowire.
 19. The biosensor apparatus of claim 16 whereinsaid sensing element is a sensing ion channel and wherein said sensingion channel is a protein pore in said lipid bilayer wherein said proteinpore is sensitive to specific agents.
 20. The biosensor apparatus ofclaim 16 wherein said sensing element is a sensing ion channel andwherein said sensing ion channel is a protein pore in said lipid bilayerwherein said protein pore is sensitive to a full spectrum of biowarfareagents including bacteria, viruses and toxins.
 21. The biosensorapparatus of claim 16 wherein said sensing element is a sensing ionchannel and wherein said sensing ion channel is a protein pore in saidlipid bilayer wherein said protein pore is sensitive to a full spectrumof health related agents including bacteria, viruses and toxins.